Nuclear Force

The nuclear force is the force between protons and neutrons , subatomic particles that are collectively called nucleons. The nuclear force is responsible for binding protons and neutrons into atomic nuclei. Neutrons and protons are affected by the nuclear force almost identically. Since protons have charge +1 e, they experience a strong electric field repulsion that tends to push them apart, but at short range the attractive nuclear force overcomes the repulsive electromagnetic force. The mass of a nucleus is less than the sum total of the individual masses of the protons and neutrons which form it. The difference in mass between bound and unbound nucleons is known as the mass defect. Energy is released when some large nuclei break apart, and it is this energy that is used in nuclear power and nuclear weapons.

The nuclear force is powerfully attractive between nucleons at distances of about 1 femtometer between their centers, but rapidly decreases to insignificance at distances beyond about 2.5 fm. At distances less than 0.7 fm, the nuclear force becomes repulsive. This repulsive component is responsible for the physical size of nuclei, since the nucleons can come no closer than the force allows. By comparison, the size of an atom, measured in angstroms (Å, or 1.0 × 10−10 m), is five orders of magnitude larger. The nuclear force is not simple, however, since it depends on the nucleon spins, has a tensor component, and may depend on the relative momentum of the nucleons.

Nuclear forces are of two types namely

1. Strong Nuclear Force

2. Weak Nuclear Force.

Nuclear forces are independent of the charge of protons and neutrons. This property of nuclear force is called charge independence. It depends on the spins of the nucleons that is whether they are parallel or no and also on the non central or tensor component of nucleons.

Strong Nuclear Force

Strong nuclear force is about 100 times stronger than electromagnetism. These forces is also known as strong interactions.

Strong nuclear forces can be applied in two aspects: One is on Larger Scale and other on Lower Scale.

1. On larger scale of about 1 to 3 fm distance, it is the force that binds the nucleons together to form nuclei.

2. On smaller scale of abut less than 0.8 fm distance, it is the force that binds quarks together to form nucleons that is protons and neutrons and also other particles like hadrons.

Weak Nuclear Force

Weak Nuclear Force is one of the four fundamental force. Electromagnetic force, gravitational force and strong nuclear force are the other forces.

Weak Nuclear Force is caused by the emission or exchange of W and Z bosons. Weak nuclear forces are very short range because of the heaviness of the W and Z particles. Weak nuclear force results in the change of one type of quark to another type. This is also known as change of flavor / flavor change of quarks.

Weak nuclear force is of two types:

1. Charged current Nuclear Force

2. Neutral current Nuclear Force.

Charged current nuclear force is so called because this force is carried by electric charge carriers i.e. W+ and W- boson particles.

These forces occurs in many reactions namely,

1. Radioactive decay

2. Beta decay

3. Burning of sun

4. Initiating the process of hydrogen fusion in stars.

5. In production of deuterium

6. Radiocarbon dating and

7. Radio luminescence.

Charged Current Nuclear Force

• A charged electron or muon (lepton) with -1 charge absorbs W+ particle of charge +1 and is converted into neutrino of charge zero. Type of neutrino will be the same as that of lepton.

• A down quark can be converted into up type quark by releasing W- particle.

• An up type quark is converted into down type by absorbing W- particle or emitting W+ boson particle.

• A W boson particle is not stable. Therefore it will decompose or decay in a short time.

Current Nuclear Particle

A quark or lepton can emit or absorb Z boson particle of zero charge. Z boson is also unstable hence decomposes very soon.

It can transform a neutron into proton and a proton into neutron.

It is responsible for radio active decay of particles. It initiates the process of hydrogen fusion at stars. It is also responsible for beta decay which is a form of radioactivity. It is also responsible for production of deuterium and helium from hydrogen which helps in burning of sun and powers the sun’s thermonuclear energy. It is also possible to perform radio carbon dating with weak nuclear force since C – 14 decays into N – 14 due to weak nuclear force. Weak nuclear force can also create radio luminescence. It also helps in the formation of heavy nucleus.